[Single] Interesting Spirit card.

[Bringerofcake]

The Fine Line

Continuous Spell

Once per turn, you can Normal Summon or Set a Spirit Monster in addition to your regular Normal Summon or Set. You cannot Tribute Summon monsters with this effect.

 

So?

[King of Nothing]

I think it should have an additional effect, like having to pay lifepoints equal to its level times 100. I can see some real spam going on if there isn't a side effect.

[Umbra]

Spirit Monarchs, maybe?

 

Psychics have Brain Research Lab, which is a more balanced version of this. For one, that is a Field Spell, which limits you to one. The Fine Line works in multiples, allowing you to basically swarm with Spirits every turn, in addition to whatever else you're summoning. Add a "You can only control 1 'The Fine Line'." sentence or something similar, and it'd be fine.

[CrabHelmet]

Multiple copies of this won't have any effect unless you have two of these plus three low-level Spirits. A five-card combo like that isn't threatening, especially when you consider that you could just as well replace one copy of this card with something like Dimension Hole that keeps the Spirit in play forever, and the effect would be similar.